The invention relates to information transmission systems and, more particularly, to the structure and operation of a modulated input signal filter.
Many new commercial applications require electronic devices that are able to communicate while maintaining low power consumption. Mobile devices are less convenient if large battery requirements increase their size or weight. Devices mounted on or in automobiles that operate when the engine is inactive must also be able to operate with only low power in order, for example, to avoid draining a car battery.
Electronic devices can communicate using modulated signals. A characteristic of an electronic signal, e.g., amplitude, frequency, phase, etc., is modified in a pattern that corresponds to information. Such modification is referred to as modulation. One type of modulation is pulse width modulation. Pulse width modulation uses a pattern defined by duty cycle to correspond to zeros and ones. Duty cycle is the ratio of the time that a signal is in a first state to the time that the signal is in a second state during a specific time interval. For example, a signal with a high state and a low state is used for digital communication. An interpretation of 25% of time in the high state as a one and 75% of the time in the high state as a zero is one implementation of pulse code modulation.
The modulated electronic signal is then transmitted and received. The receiver compares the modifications to the pattern to determine the information that was intended to be transmitted. The receiver, however, does not analyze an exact copy of the modulated signal. Electronic devices near the receiver as well as physical imperfections in the transmission and reception equipment and the transmission medium combine to add a random signal referred to as noise.
The noise added to the modulated signal, noise can be negative as well as positive, can complicate or create errors in the communication where the noise is significant in relation to the amount of modification corresponding to information. In situations where low power is desirable, noise can also cause a receiver to operate at a higher power level as it attempts to determine what information was intended to be sent by the noise signal. A receiver may successfully determine that the noise does not represent information, but spend an undesirably significant amount of power in producing that output. In situations where the microcontroller in the receiver is performing a background task, processing time is undesirably diverted to analyze noise.
Some receivers for devices such as garage doors pass the digital signal corresponding to the modulation on to a microcontroller that determines whether the signal is authorized to actuate the device. Increased levels of security can correspond to greater power use in the microcontroller. A sleep mode can be used to reduce the power consumption of the microcontroller when no signal is present.
U.S. Pat. No. 5,463,662 discloses an apparatus for reducing errors in data caused by noise. A signal whose amplitude is modified in accordance with information is sampled by an analog-to-digital converter to provide digital signals representative of the sample. A low frequency offset is then subtracted from the digital signals. The resulting signal is compared to its average level and the comparison output is used as a control signal to determine when a blanking circuit will blank the digital signal. The selective removal of noise effects can reduce errors, but does not significantly reduce the amount of power used by the receiver in detecting valid signals.
The present invention is directed to a modulated input signal filter, a method filtering, and systems employing the apparatus or method.
In an embodiment of the modulated input signal filter of the present invention, a switch responds to the input signal by coupling one of two circuits to a gate. The input signal is also coupled to the gate. The gate operates to either pass through the input signal as an output or to output a default signal regardless of the input signal state. One of the circuits coupled by the switch influences the gate over time to pass through the input, while the other circuit influences the gate over time to output the default signal.
In a more specific embodiment of the present invention, the input signal is a voltage and has two states corresponding to lower and higher voltage ranges. Each of the two circuits includes a capacitor, but one circuit drains the capacitor with a current source
while the other charges the capactor with a current source. The gate receives the voltage currently on the capacitor as an input. When that voltage is in a high state, the gate passes the input signal through to its output. When, the capacitor voltage is in a low state, the gate outputs a default signal. A high voltage input signal couples the charging current source to the capacitor and results in the input signal being passed through the gate in a specific period of time that depends on the initial voltage of the capacitor. In one embodiment, the gate passes through the input signal within 3 milliseconds of being connected to the charging circuit.
In one system embodiment of the present invention, the input signal is received at an antenna. The output signal of the gate is coupled to a microcontroller. The microcontroller is coupled to an automobile door lock mechanism to unlock the automobile door when a specific signal is received. In a more specific embodiment, the microcontroller has a sleep mode that is entered after receiving the default signal for a specified time from the gate output. The sleep mode uses less power than than mode is which the microcontroller analyzes received input signals for the specific signal.
In another system embodiment of the present invention, the input signal is received at an antenna. The output signal of the gate is coupled to a microcontroller. The microcontroller is coupled to a pet door lock mechanism to unlock the pet door when a specific signal is received. In a more specific embodiment, the microcontroller has a sleep mode that is entered after receiving the default signal for a specified time from the gate output. The sleep mode uses less power than than mode is which the microcontroller analyzes received input signals for the specific signal.
In a method embodiment of the present invention, an input signal is filtered by the application of specific steps. The input signal is received by an antenna. The ratio of time that the input signal is high relative to the time that the input signal is low is measured. The input signal is blocked from reaching an output if the input signal has not been in a high state for a specified length of time. The input signal is blocked if the measured ratio is less than a specified ratio. If the input signal is not blocked it is transmitted to the output. The output is connected to a circuit with sleep functionality.
A feature of the invention is filtering an input signal.
Another feature is operating communications systems at low power.
An advantage of the present invention is setting a receiver to ignore noise based on length characteristics of the noise.
Another advantage is ignoring noise based on the duty cycle of the noise.
Still another advantage is decreasing the power used by a signal analyzing microcontroller or circuit by blocking noise signals.
Another advantage is allowing an override to selectively impose a time delay on signal receipt.
Other and further features and advantages will be apparent from the following description of presently preferred embodiments of the invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawings. Not all embodiments of the invention will include all the specified advantages. For example, one embodiment may only ignore noise based on the duty cycle of the noise, while another only decreases the power used by the signal analyzing microcontroller.